Andrew McCutchen and the Pirates play a key three-game series against the Cardinals this weekend in Pittsburgh. / Jeff Curry, USA TODAY Sports

by Jorge L. Ortiz, USA TODAY Sports

by Jorge L. Ortiz, USA TODAY Sports

As the calendar turns from August to September, the baseball landscape will look decidedly different â?? in who's switching teams, emerging from the minor leagues and even in how the game is played. USA TODAY Sports' Jorge L. Ortiz takes a look at the factors that will impact the final maneuvering before a sprint to the finish:

Races: Going into the weekend, the National League action was focused on the Central, which has emerged as the league's power division and figures to produce three of the five playoff entries. Only a major September slumber would keep the Atlanta Braves and Los Angeles Dodgers from claiming the East and West, respectively.

The Central is a tossup, though, making this weekend's three-game series pitting the St. Louis Cardinals at the Pittsburgh Pirates the majors' most compelling matchup. The last time these clubs met, also at PNC Park a month ago, the Pirates won the first four in a rare five-game series.

The Cincinnati Reds lurk a bit behind after losing two of three in St. Louis, but remain in prime position for the second wild card.

The American League is less defined, although it's hard to envision the Detroit Tigers losing their grip on the Central, particularly after Thursday's thrilling walkoff victory over the Oakland Athletics.

The stunning five-run comeback prevented a four-game sweep, but the A's may have picked up momentum anyway after battering Detroit's top four starters â?? Max Scherzer, Justin Verlander, Anibal Sanchez and Doug Fister â?? for 19 earned runs in 20 innings. None pitched more than five innings.

On Friday, the A's open a 10-game homestand with a weekend series against the Tampa Bay Rays, who are striving to keep pace with the AL East-leading Boston Red Sox. That's followed by a three-game set with the Texas Rangers, who have taken over in the West by going 22-6 since July 29.

Acquisitions: The Pittsburgh Pirates' addition of outfielder Marlon Byrd and catcher John Buck on Tuesday serves as proof you can still trade for significant contributors at this time of year, even if you have to overcome more impediments. But there's increasing pressure to make any moves before Sunday, when the arrival of September will render players brought in from outside the organization ineligible for the playoffs.

Friday, the action picked up considerably.

The St. Louis Cardinals dealt for former Milwaukee Brewers closer John Axford. The Baltimore Orioles completed a deal for right-handed - but slumping - power hitter Michael Morse.

And Jason Kubel - designated for assignment by the Arizona Diamondbacks - landed with the Cleveland Indians, who could use his left-handed bat down the stretch.

There remains an active market for veteran hitters, with the New York Yankees, Pirates, Rangers and Baltimore Orioles looking to upgrade their offenses. That puts in play sluggers like Justin Morneau.

This is the time of year when clubs put in claims almost as much to block a player from going to an opponent as to bolster their rosters. That was the case when the San Francisco Giants picked up Cody Ross at the end of the 2010 season, and it worked out pretty well. Ross didn't do much in 33 regular-season games with the Giants, but then took off in the postseason and became the NLCS MVP.

September call-ups: Several of the names familiar to prospect watchers have already trickled in.

Red Sox shortstop Xander Bogaerts, 20, made his major league debut on Aug. 20. A's right-hander Sonny Gray made an impression by throwing eight innings of four-hit ball in his second start. Jake Odorizzi replaced an ineffective Jeremy Hellickson in the Rays rotation. And Taijuan Walker, 21, just got promoted by the Seattle Mariners.

More are on the way as rosters expand on Sunday, and their impact could be as limited as a bench role or as meaningful as a regular spot in the lineup, depending on what dictates their call-up and how they perform.

Reds speedster Billy Hamilton hasn't burned the basepaths at Class AAA Louisville the way he did last season at Class A and AA when he set a record with 155 stolen bases. He still has 73, though, and could prove a valuable weapon in the playoff chase.

Other call-ups who could be factors in September include the A's Michael Choice, the Orioles' Jonathan Schoop, the Red Sox's Jackie Bradley and the Indians' Trevor Bauer.

Injury matters: Boston could get a late-season boost without making any deals if starter Clay Buchholz returns on Sept. 10 as scheduled and shows anywhere near the form that saw him go 9-0 with a 1.71 ERA before being sidelined since early June by a shoulder injury.

Likewise, the suddenly stumbling Rays are hoping for a similar push from Matt Moore's return to the rotation, expected Tuesday. Tampa Bay players and staffers headed west for the beginning of a 10-game trip sporting the colors of their favorite college football teams, a nod to the beginning of the season from ever-inventive manager Joe Maddon.

The A's pitching staff, which had been wobbling going into the Detroit series, just welcomed Bartolo Colon and Brett Anderson back from the disabled list. And former Rangers closer Neftali Feliz just announced he'll be joining the club in Oakland after missing the first five months of the season recovering from Tommy John elbow surgery.